Aggregation-induced emission enhancement -active triarylamine-based polyamides containing fused ring groups towards electrochromic smart window and sensor for HCl and TNP

Article abstract of DOI:10.1016/j.dyepig.2020.108799

A series of new polyamides (PAs) were designed and synthesized based on two novel triarylamines (TAA) with fused ring groups via phenyl bridge through the Suzuki coupling reaction. These novel PAs have amorphous structure and excellent thermal stability, with a carbon residue rate of up to 70percent at 800 °C in nitrogen atmosphere. In the process of electrochemical oxidation, there is no obvious recessionary in current and transmittance over 1000s with a cycle time of 10s, which showing high contrast and excellent cycle stability. And the electrofluorochromic (EFC) performance can also be adjusted by being applied voltage. 1NAT-CA and 9AAT-CA have solvatochromic effect in absorption, fluorescence (PL) in solvents, 1NAT-6F and 1NAT-BA have aggregation-induced emission enhancement (AIEE) properties in solid state. The kind of multifunctional integrated PAs show characteristics of responding to voltage, explosive and hazardous gas stimuli and the stimuli-responsive mechanisms are investigated, which have the prospect of application in photoelectric sensors, explosive detectors and high-contrast displays.

Full text of DOI:10.1016/j.dyepig.2020.108799

Dyes and Pigments 184 (2021) 108799
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: http://www.elsevier.com/locate/dyepig
Aggregation-induced emission enhancement -active triarylamine-based
polyamides containing fused ring groups towards electrochromic smart
window and sensor for HCl and TNP
a
a
a
a
a
a
a
Dongxu Li , Yan Yang , Caiyu Yang , Wei Zhang , Yan Wang , Xiaoxue Lin , Yanyu Gao ,
a
a
,
*
b
Xinying Lv , Haijun Niu , Wen Wang
a
Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, Department of Macromolecular Science and Engineering, School of Chemical,
Chemical Engineering and Materials, Heilongjiang University, Harbin, 150086, PR China
b
School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, 150080, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
A series of new polyamides (PAs) were designed and synthesized based on two novel triarylamines (TAA) with
fused ring groups via phenyl bridge through the Suzuki coupling reaction. These novel PAs have amorphous
Polyamide
Electrochromic
Electrofluorochromic
AIEE
◦
structure and excellent thermal stability, with a carbon residue rate of up to 70% at 800 C in nitrogen atmo-
sphere. In the process of electrochemical oxidation, there is no obvious recessionary in current and transmittance
over 1000s with a cycle time of 10s, which showing high contrast and excellent cycle stability. And the elec-
trofluorochromic (EFC) performance can also be adjusted by being applied voltage. 1NAT-CA and 9AAT-CA have
solvatochromic effect in absorption, fluorescence (PL) in solvents, 1NAT-6F and 1NAT-BA have aggregation-
induced emission enhancement (AIEE) properties in solid state. The kind of multifunctional integrated PAs
show characteristics of responding to voltage, explosive and hazardous gas stimuli and the stimuli-responsive
mechanisms are investigated, which have the prospect of application in photoelectric sensors, explosive de-
tectors and high-contrast displays.
Sensor
1
. Introduction
Electrochromic materials of TAA-based are widely used in high-
color contrast [10–14]. The band gap of TAA-based polymers can be
precisely adjusted through structural control and different modifications
of TAA and comonomers. Compared with the previous reports, this time
the fused ring groups such as naphthyl and anthranyl are directly con-
nected to TAA units to form larger conjugated areas and longer conju-
gated chains while the twist angles between the TAA skeleton and the
performance electronic displays, smart windows, and wearable devices
as new energy-saving and widely used environmentally-friendly smart
materials [1,2]. The group of Liou, Hsiao, Niu, Liaw, Chao, Zhao and
many others groups researched and reported many high-quality EC
materials with unique properties containing TAA units [3–9]. The EFC
performance is crucial to the application in the dark field, therefore the
PL is anticipated for the EC materials, and the introducing photo-
luminescecnt chromophore is sound strategy. The propeller-shaped TAA
molecule is a good hole-transporting material because of its high sta-
bility as the corresponding radical cation, strikingly high oxidation po-
tential and interesting photoelectric activity. Therefore, TAA-based
high-performance derivatives have been widely used in electrochromic
g
fused ring groups help to regulate energy band gaps (E s).
Aromatic and aliphatic PAs have been extensively studied for their
PL, EC properties, and internal charge transfer (ICT) in polymers. Among
EC materials, PAs are recognized engineering plastic with high thermal
stability, corrosion resistance, flame resistance, high mechanical
strength and good ductility [15–17]. But the rigidity and strong inter-
molecular interaction of the backbones lead to low solubility and diffi-
culty in processing, which limit their wide practical application [18,19].
In order to increase the solubility and to enhance their process ability
without reducing the thermal stability and mechanical strength of the
PAs, TAA group with a large volume is introduced into the polymer
structure, which provides an effective strategy for the preparation of
(
EC) materials, PL sensor. Especially, TAA-based polymers in the field of
EC device have attracted the focus of scientists due to their fast
switching response time, excellent switching cycle stability, and high
*
Corresponding author.
E-mail address: haijunniu@hotmail.com (H. Niu).
https://doi.org/10.1016/j.dyepig.2020.108799
Received 23 May 2020; Received in revised form 10 August 2020; Accepted 18 August 2020
Available online 25 August 2020
0
143-7208/© 2020 Elsevier Ltd. All rights reserved.

D. Li et al.
Dyes and Pigments 184 (2021) 108799
Scheme 1. Synthesis routes of the monomers.
solution-processable PAs which provides practical application in
large-area electro-optical devices [20–23].
fields of electricity, optics, biological sciences and other fields has
caught attention intensely. Some nitroaromatic compounds are toxic
pollutants or dangerous explosives, which cause great harm to the
environment and threaten human health. 2,4,6-trinitrophenol (TNP) is a
common pollutant in soil and groundwater, which seriously threatens
On the other hand, since the AIE effect was reported by Tang in 2001
[
24,25], the potential application of high-efficiency and excellent
luminescent materials in the solution aggregated or solid state in the
1
13
Fig. 1. (a) H NMR, (b) C NMR, (c) C–H HSQC spectra of 1NATAA in CDCl
3
, (d) FTIR spectra of 1NATAA and 9AATAA.
2

D. Li et al.
Dyes and Pigments 184 (2021) 108799
Scheme 2. Synthesis routes of PAs.
◦
the cleanliness of the water source and the safety of the soil [26].
Hydrogen chloride (HCl) is a kind of hazardous gas that has strong
irritation to the upper respiratory tract, eyes, skin, mouth and respira-
tory mucosa. However, traditional methods for detecting TNP or HCl are
limited by problems such as high cost, complicated operation, and low
sensitivity, which are difficult to detect quickly. Therefore, the devel-
opment of rapid, low-cost and high-sensitivity fluorescent sensing ma-
terials are of great significance [27,28]. By taking advantage of the
mechanism that TNP or HCl can effectively quench the PL of TPA-based
PAs, PAs can be used as PL sensor to detect TNP and HCl more
intuitively.
followed by 115 C for 5 days under nitrogen atmosphere; the reaction
progress was monitored in real time by TLC method. After the reaction
was cooled to room temperature, the solution was poured into 1 L of cold
water and the precipitate was collected. The dried precipitate was
recrystallized from mixture of ethyl acetate and hexane (1:9). The
crystalline product was purified by chromatography on silica gel with
mixture of ethyl acetate and petroleum ether (1:3), and 4-(naphthalen-1-
yl)-N,N-bis(4-nitrophenyl) benzenamine (1NNTAA) of the light brown
◦
red crystals was obtained, 35% of yield (mp:217.5–219.2 C).
ꢀ 1
1
2
1NNTAA: FTIR (KBr, cm ): 1376, 1587 (-NO s). H NMR (400
MHz, CDCl
3
), δ (ppm) = 7.97–7.94 (d, 4H, H
.62–7.58 (t, 2H, H ), 7.52–7.50 (m, 5H, H + H
.42–7.40 (d, 2H, H
a
), 7.93–7.91 (d, 1H, H
g
),
),
7
7
f
b
i
), 7.48–7.46 (d, 2H, H
).
d
e
), 7.32–7.30 (d, 2H, H
c
), 7.28–7.27 (t, 1H, H
h
2
. Experimental section
Finally, 1NNTAA (2.5 mmol, 1.1521 g), 10% of Pd/C (30 mg), and
1
20 mL of ethanol as solvent were added to a three-necked round bottom
2
.1. Synthesis of monomers
◦
flask, and hydrazine was dropped and reacted for 24 h at 80 C under
2
.1.1. 4-(Naphthalene-1-yl)-N,N-bis(4-aminophenyl)-benzenamine
(
1NATAA)
The synthetic route is shown in Scheme 1. 4-bromoaniline (8.611 g,
0 mmol), 4-fluoronitrobenzene (8.4674 g, 60 mmol) and CsF (7.5951 g,
0 mmol) were added to a round bottom three-necked flask and 120 mL
5
5
purified DMSO as solvent. Under nitrogen atmosphere, the magnetic
◦
stirring kept on the temperature which was raised to 130 C for 24 h; the
reaction progress was monitored in real time by thin layer chromatog-
raphy (TLC) method. After the reaction was cooled to room temperature,
the solution was poured into 1 L of cold water with constant stirring and
yellow precipitate was collected [29,30]. The dried precipitate was
recrystallized from acetic acid to obtain yellow crystal of Br-TPA, 53% of
yield, (mp: 309.1–311.6 C). The FTIR and 1H NMR spectra of Br-TPA
are shown in Fig. S1.
◦
Br-TPA: FTIR (KBr, cm 1): 1347, 1582 (-NO
CDCl ), 7.56–7.54 (d, 2H, H
), δ (ppm) = 8.17–8.15 (d, 4H, H
.16–7.1 (d, 4H, H ), 7.06–7.04 (d, 2H, H ).
After that,1-naphthylboronic acid (1NPB, 15 mmol, 2.5831 g) and
monomer Br-TPA (10 mmol, 4.1379 g) was added to a Schlenk flask with
0 mL of DMF as solvent. Next, 0.01164 g (0.01 mmol) Pd(PPh , 20 mL
of K CO (2.5 N) solution, 10 mL of ethanol were charged in turns,
ꢀ
s), H NMR (400 MHz,
),
1
2
3
a
d
7
b
c
8
3 4
)
2
3
Fig. 2. FTIR spectra of PAs.
3

D. Li et al.
Dyes and Pigments 184 (2021) 108799
Table 1
TGA and molecular weights of the PAs.
a
a
a
c
c
d
PAs
T
5%
T
10%
T
20%
Char
Yield
M
w
M
n
PDI
DP
◦
◦
◦
b
Code
C
C
C
(Da)
(Da)
(
t
W %)
1
1
1
9
9
9
NAT-
327
334
338
295
326
329
363
378
373
353
432
348
511
552
429
443
615
424
54
70
58
55
72
54
2.7 ×
1.4
1.95
1.96
1.92
1.95
1.95
1.93
19
25
12
15
27
13
4
6
F
10
×
4
1
0
NAT-
BA
2.9 ×
1.5
4
10
×
4
1
0
NAT-
CA
1.2 ×
6.3
4
10
×
3
1
0
AAT-
2.4 ×
1.2
4
6
F
10
×
4
1
0
AAT-
BA
3.6 ×
1.8
4
10
×
4
1
0
AAT-
CA
1.5 ×
7.6
4
10
×
3
1
0
a
d
The T of polymer is the temperature at which the polymer loses 5%, 10%
and 20% weight.
b
◦
Measured at 800 C in nitrogen.
c
Dispersity: M
w
/M
n
.
d
Degree of polymerization.
Table 2
Optical properties of solutions and films of the PAs.
a
PAs Code
In solution λ (nm)
As film λ (nm)
Abs
PL
Φ
PL
Abs
Abs
PL
Φ
PL
b
max
max
(%)
max
onset
max
(%)
1
1
1
9
NAT-6F
NAT-BA
NAT-CA
AAT-6F
349
353
324
362
364
321
513
523
495
539
450
553
2.4
2.1
815
843
828
798
821
811
481
443
379
501
495
376
518
470
493
525
468
491
21.4
21.9
38.2
25.7
24.1
40.4
37.4
18.1
7.7
Fig. 3. (a) X-ray diffraction patterns of PAs. (b) Thermogtravimetric analysis
9AAT-BA
9
AAT-CA
39.8
2
curves of PAs in N .
a
b
ꢀ 5
ꢀ 1
Measured in NMP solution (1 × 10 mol L ).
Calculated with quinine sulfate as a standard reference (ΦPL = 54.6%).
nitrogen atmosphere. After the reaction, the Pd/C was removed by hot
filtration to collect the liquid. The liquid was poured into 1 L of distilled
water to collect the off-white precipitate and the solid was dried in
◦
◦
vacuum at 28 C, 81% of yield (mp:159.2–164.5 C).
of NMP solution in 25 mL three-necked round bottom flask. Then 1.2 mL
of pyridine, 3 mL of triphenyl phosphite (TPP) and 0.25 g CaCl were
The spectra of NMR and FTIR of 1NATAA are shown in Fig. 1. FTIR
2
(
KBr, cm 1): 3360, 3442 (N–H s), H NMR (400 MHz, CDCl
ꢀ
1
3
), δ (ppm) =
added in order. Under nitrogen atmosphere, the magnetic stirring was
kept on the reaction mixture was stirred for 10 min at room temperature.
8
.05–8.02 (d, 1H, H
.49–7.42 (m, 4H, H
), 6.99–6.97 (d, 2H, H
e
), 7.88–7.86 (d, 1H, H
+ H ), 7.27–7.25 (d, 2H, H
), 6.67–6.65 (d, 4H, H
g
), 7.80–7.78 (d, 1H, H
f
),
7
h
i
d
), 7.05–7.03 (d, 4H,
◦
Then the reaction temperature was raised to 130 C for 3 h. The viscous
H
1
b
c
a
), 3.71 (s, 4H, –NH
2
).
solution obtained after the reaction was slowly poured into 300 mL of
methanol to obtain a fibrous solid precipitate. The precipitate was
3
2
5
C NMR (100 MHz, CDCl
3
), δ (ppm) = 148.4 (C ), 142.7 (C ), 140.3
9
13
10 4 8 7
(
C ), 139.2 (C ), 133.9 (C ), 131.8 (C ), 131.4 (C ), 130.3 (C ), 128.2
◦
collected in vacuum at 45 C after Soxhlet extraction to remove low
1
4
3
15
11
12
6
(
C
), 127.2 (C ), 126.9 (C ), 126.7 (C ), 125.4 (C ), 118.6 (C ),
molecular weight oligomers and a small amount of residual monomers.
The FTIR spectrum of 1NAT-6F agrees with the molecular structure
1
+
1
16.2 (C ). HRMS (ESI-MS): Found [M + MeCN + H] 443.2144; mo-
lecular formula C30 requires 443.2157.
H
26
N
4
ꢀ 1
of polymer which is shown in Fig. 2. FTIR (KBr, cm ): 3309 (N–H
The synthetic route of 4-(anthraceneboronic-9-yl)-N,N-bis(4-amino-
phenyl)-benzeneamine (9AATAA) was shown in supporting
information.
stretching of amide), 1672 (carbonyl stretch of amide), 1590 (C–
C
–
stretch of benzene ring skeleton), 1250 (C–N stretch of amide), 1174
1
(
C–F stretch of amide). H NMR (400 MHz, CDCl ); δ (ppm) = 8.64 (N–H
3
of amide), 6.82–8.26 (aromatic ring of benzene). Other PAs were also
prepared as described above (shown in Fig. S3.).
2
.2. Synthesis of PAs
The synthetic route of Poly (4-(naphthalen-1yl)-N,N-bis(4-amino-
phenyl) benzenamine-alt- 2,2- bis(4-carboxyphenyl) (1NAT-6F) is used
as a general route to synthesize all PAs (in Scheme 2) [31]. 6 F (0.4887 g,
1
.25 mmol) and 1NATAA (0.5124 g, 1.25 mmol) were dissolved in 3 mL
4

D. Li et al.
Dyes and Pigments 184 (2021) 108799
3
. Results and discussions
solubility is summarized in Table S1. According to previous reports, the
solubility of PAs is influenced by combination of the accumulation of
polymer chains, the interaction between rigid molecules, and the sym-
metry of the polymer backbone. PAs can be easily dissolved in DMF,
DMSO and NMP which are polar solvents with stirring gently at room
temperature, contrast to be less soluble in less polar solvents such as
toluene (Tol) and toluene. As expected, these amorphous PAs have
better solubility in polar solvents, and it is expected that a large-area of
polymer films will be formed in practical application through process of
roll-to-roll, spraying, spin coating, dripping, dip coating [32]. The
amorphous state of the polymers and good solubility in polar solvents (in
Table S1.) can be attributed to a large amount of internal volume be-
tween the polymer chains provided by the TPA units which are
non-planar molecules and the twist angles between the TPA units and
the fused ring groups.
3
.1. Synthesis
The fused ring-modified TAA monomers were obtained by reducing
the product of reaction of Br-TPA and arylboronic acid through Suzuki
coupling reaction via Pd/C (in Scheme 1.). There are few reports on
connecting fused rings directly to TPA side groups to form larger bulky
1
13
structures. The FTIR, H NMR, C NMR, C–H HSQC, and ESI-MS tech-
niques are used to confirm that two target monomers are synthesized
successfully. The amine group shows two distinct and typical N–H
stretching characteristic vibration bands around 3357 cm and 3442
cm 1. And the PAs were polycondensed by diamines monomers and
ꢀ
1
ꢀ
various dicarboxylic acids. The FTIR spectra show typical N–H (3308-
ꢀ 1
–
–
ꢀ 1
ꢀ 1
)
3
384 cm ), C
O (1667-1680 cm ) and C–N (1240-1250 cm
1
stretching vibration bands and H NMR spectra confirm the polymer
structure.
The thermal properties of PAs with different fused ring groups in the
pendant group were investigated by thermogtravimetric analysis (TGA)
in N
2
atmosphere. As shown in Fig. 3b, the carbon residual ratio of these
◦
PAs at 800 C is above 50%, and the char yields of 1NAT-BA and 9AAT-
BA are more than 70%, which show good high temperature resistance
3
.2. XRD and solubility
◦
properties. And the char yields at 800 C are summarized in Table 1. By
As shown as in Fig. 3a, these PAs have similar broad peaks in the
◦
◦
comparison, it is found that the rigid structure of the pendant group
makes it difficult to decompose in the high temperature region [33].
range of 2θ from 17 to 19 in X-ray diffraction (XRD) patterns, which
mean that these PAs are amorphous which is attributed to the disorder
packing form of PAs. 10 mg of these PAs was dissolved in different
solvents with stirring at room temperature to test the solubility, and the
Fig. 4. (a) The UV–vis and PL spectroscopy of PAs of concentration 1 × 10ꢀ 5 mol/L in NMP. (b) The PAs films and PAs in NMP solution were photographed under
irradiation of 365 nm UV light. (c) The calculated electron density in the frontier molecular orbitals of the dimers. (d) The CIE1931 coordinates (X,Y) of PAs in
NMP solution.
5

D. Li et al.
Dyes and Pigments 184 (2021) 108799
2
76–292 nm (in Fig. 4a.). According to previous literature reports, the
π
- * transition between the aromatic ring of the TPA skeleton and cen-
π
tral nitrogen atom is the reason why the PAs have absorption peak at
2
76–292 nm while the intramolecular charge transfer (ICT) produced in
the PAs backbone resulted in strong UV absorption at 321–375 nm [34].
The PL emission spectra in NMP exhibit maximum emission peak at
4
50–553 nm (in Fig. 4a.), and the PAs films and PAs in NMP solution are
photographed under irradiation of 365 nm UV light (in Fig. 4b.) and the
CIE1931 coordinates are shown in Fig. 4d. The PL quantum efficiency
(
Φ
PL) of PA is calculated by comparison with the standard quinine sul-
1NAT-CA (37.4%) >
1NAT-6F (2.4%) >
1NAT-BA (2.1%) (in Table 2.). It is clear that 1NAT-CA shows stronger
fate. The order of ΦPL is ΦPL
Φ
Φ
-
9AAT-CA (39.8%) > ΦPL
-
PL
-
-
9AAT-6F (18.1%) > ΦPL
-
9AAT-BA (7.7%) > ΦPL
-
PL
PL intensity than 1NAT-6F, and the ΦPL (37.4%) of 1NAT-CA is higher
than that of 1NAT-6F (2.4%) because the alicyclic structure in the
polymer as an electron-donor group can effectively reduce the conju-
gated structure length and the charge transfer along the long chain. In
short, the less PL intensity of 1NAT-6F is due to strong charge transfer
(
CT). To further explain this phenomenon better, it is more intuitive to
draw conclusions by theoretically calculating the density of the frontier
electrons of the dimers of 1NAT-CA and 1NAT-6F (in Fig. 4c.). The
highest occupied molecular orbital (HOMO) locates in TAA moiety
which acts as an electron donor while the lowest unoccupied molecular
orbital (LUMO) locates in hexafluoroalkyl moiety which acts as an
electron acceptor. Due to the transition from the ground state to the
excited state while the electrons transfer from TAA to 1NAT-6F moiety,
demonstrating strong electron transfer inside the polymer chain. In
obvious contrast, the HOMO of 1NAT-CA is in the TAA moiety but the
LUMO locates in the cyclohexyl moiety, which can be explained by the
fact that the aliphatic structure disturbs the conjugated structure of the
polymer chain and reduces the charge transfer effect inside the chain [5,
3
1
5,36]. 9AAT-CA emits strong PL due to the same mechanism as
NAT-CA. 9AAT-6F and 9AAT-BA also emit weak PL probably due to the
stronger CT process from donor to acceptor groups. The solution and
solid films of PAs exhibit different colors due to the solvatochromic ef-
fect and the introduction of TAA luminogens. The solid film emits
different colors of light under irradiation of 365 nm UV light (the order
from left to right is 1NAT-6F, 9AAT-6F, 1NAT-BA, 9AAT-BA, 1NAT-CA
and 9AAT-CA.) (in Fig. 4b.)
Fig. 5. (a) The UV–vis absorption and PL emission spectra of 9AAT-CA. (b) A
(
))
2
ε
ꢀ 1
n ꢀ 1
plot of (
νA ꢀ
ν
F) versus the orientation polarizability (Δf =
ꢀ
2
.
2
ε
+1
2n +1
Interestingly, the ΦPL of solid films of 1NAT-6F and 1NAT-BA
respectively reach 21.4% and 21.9%, which are much higher than the
Φ
PL of their solution. The higher ΦPL of solid is due to the aggregation of
PAs molecules containing TAA which decreases the benzene rotating
and descends the losing of energy (AIEE effect) (in Fig. 4b.). The slight
enhancement of ΦPL for 1NAT-CA and 9AAT-CA from the solution to the
film is due to the AIEE effect being stronger than the aggregation-caused
quenching (ACQ) effect [37].
3
.3.2. Solvatochromic effect
To investigate the influence of the solvent with different polarity on
the position of PL of PAs, the absorption and PL spectra of 1NAT-CA and
ꢀ
5
ꢀ 1
9
AAT-CA solution with concentrations of 1 × 10
mol L were
researched and investigated. As shown in Fig. 5a and Fig. S4, there is no
significant change in the position of the absorption peaks at 320 nm and
3
31 nm attributed to
π
- * transition. In contrast, the emission wave-
π
lengths (λ) of the PAs are very sensitive to the polarity of the solvents.
The results are summarized in Table S2 and Table S3. The results show
that the polarity of the solvent has no significant effect on the absorption
peak position can be attributed to the PA molecule is exposed to the
same local solvent chemical environment in the ground and excited
states. By contrast, PL emission peak of 1NAT-CA and 9AAT-CA in from
the nonpolar toluene (Tol) solution to the moderately polar THF and
Fig. 6. PL spectra of 1NAT-6F mixed solutions with different water contents.
3
.3. Optical properties
3
.3.1. UV–vis absorption and PL
ꢀ 5
The UV–vis and PL spectroscopy of PAs of concentration 1 × 10
3
CHCl (Chl) solution to the highly polar ACN, DMF and DMSO solution
mol/L in NMP were measured to investigate the optical properties. As
shown in Table 2, strong UV–vis absorption of PAs exhibits PL emission
maximum at 321–362 nm, which shows relatively weak absorption at
are significantly red-shifted from 414 nm to 508 nm (for 1NAT-CA) (in
Fig. S4.) and 459 nm–570 nm (for 9AAT-CA) (in Fig. 5a.), respectively.
PL emission exhibits a strong dependence on the polarity of the solvent
6

D. Li et al.
Dyes and Pigments 184 (2021) 108799
Table 3
Electrochemical properties of the PAs.
abs
a
peak
onset
b
electro
c
electro
LUMO
c
d
quntum
HOMO
e
quntum
LUMO
e
quntum
g
e
f
PAs Code
λ
E
E
E
Eg
E
E
E
dihedral angles (θ)
onset
HOMO
◦
◦
◦
◦
◦
◦
1
1
1
9
9
9
NAT-6F
NAT-BA
NAT-CA
AAT-6F
AAT-BA
AAT-CA
481
443
379
501
495
376
0.73
0.68
0.63
0.78
0.70
0.59
ꢀ 5.08
ꢀ 5.03
ꢀ 4.98
ꢀ 5.13
ꢀ 5.05
ꢀ 4.94
ꢀ 2.51
ꢀ 2.24
ꢀ 1.71
ꢀ 2.66
ꢀ 2.54
ꢀ 1.65
2.57
2.79
3.27
2.47
2.51
3.29
ꢀ 4.72
ꢀ 4.61
ꢀ 4.66
ꢀ 4.98
ꢀ 4.78
ꢀ 4.81
ꢀ 2.18
ꢀ 2.11
ꢀ 1.56
ꢀ 2.06
ꢀ 2.12
ꢀ 1.41
2.54
2.50
3.01
2.92
2.66
3.40
45.3
42.3
42.4
55.8
51.3
44.5
a
b
c
ꢀ 5
ꢀ 1
λ
onset of PAs in NMP solution (1 × 10 mol L ).
4 4 3
Onset potential of the PAs CV curve calculated from CV vs Ag/AgCl in 0.1 M Bu NClO /CH CN.
aq
E
HOMO = (-evs Ag/AgCl + 4.35); ELUMO = EHOMO +.Eg
d
e
f
aq
E
= 1240/λonset.
g
Quantum theoretical calculation of the PAs.
The twist angles between the TPA unit and the fused ring group.
3
.3.3. AIEE effect
The solid films of 1NAT-6F and 1NAT-BA exhibit strong PL under
irradiation of 365 nm UV light which suggests that PAs have AIEE
characteristics. The previous work of Liou’s group pointed out that TAA
is AIEE-active, and the enhanced PL emission is attributed the formation
of molecular aggregates that limits the internal rotation of the molecule
[
39]. 1NAT-6F (in Fig. 6.) and 1NAT-BA (in Fig. S5.) are found to have
aggregation-induced emission effect which demonstrating to be strong
AIEE-active. Since NMP is a good solvent for PAs and PAs are insoluble
in water, the PL behavior of PAs can change from in NMP solution to in
aggregate-induced light-emitting particles solid state by increasing the
content of water component in the mixed solution. The PL emission of
ꢀ 5
1
NAT-6F in NMP solution (concentration 1 × 10 mol/L) mixed with
different water contents was investigated, and the change of PL emission
is dependence on the different water contents of the mixed solution
which are 90%, 70%, 50%, 30%, 10%, 0%, respectively. 1NAT-6F shows
extremely weak yellow light (in Fig. 6.) in pure NMP solution with the
maximum PL emission peak (λmax) is around 530 nm and the PL emission
could be adjusted by increasing the water content, accompanied by PL
emission being slightly blue shifted. The PL intensity of the mixed so-
lution increases with water content increasing and the PL intensity is the
strongest at a water content of 90% (in Fig. 6.). The increase in PL in-
tensity with the increasing of water content can be interpreted as the
AIEE effect due to molecular aggregation, which limiting the internal
rotation of molecules [24,25]. With the water content increasing
further, the PL intensity decreases which comes from the competition of
ACQ and AIEE effects. This could be explained by the further molecular
aggregation and enhanced intermolecular stack [32].
Fig. 7. (a) CV curves of 1NAT-6F, 1NAT-BA and 1NAT-CA, (b) CV curves of
9
4
AAT-6F, 9AAT-BA and 9AAT-CA on ITO/glass electrode in 0.1 M LiClO /ACN
ꢀ 1
solution at a scan rate of 50 mv s
.
with a significant red shift of the emission as increasing solvents po-
larity. When the emitting fluorophore is exposed to the solvent-relaxed
environment, a large number of charges are transferred from the amino
groups towards to carbonyl groups in the excited states resulting in a
larger dipole moment becoming in the excited state. Subsequently, the
interaction between the emitting fluorophore and the solvent becomes
stronger, which resulting in decrease of the energy of the excited state
and the lower energy level. The process can be described by the Lippert-
Mataga Eq. (1).
3
.4. Electrochemical properties
The detailed data of CV testing and quantum chemical calculations
(
) (μE
2
2
2
hc
ε
ꢀ 1
n ꢀ 1
ꢀ
μG
)
are summarized in Table 3. As shown in Fig. 7a, the oxidation potentials
of three different PAs are 0.68 V, 0.49 V, 0.71 V, respectively. And a pair
of redox peaks is corresponded to a color change (in Fig. S6.) in the
polymer films which are attributed to the oxidation of TAA to form
ν
A
ꢀ
ν
F
=
ꢀ
+ constant
(1)
is
2
3
2
ε
+ 1 2n + 1
α
In this equation, h is Planck’s constant, c is the speed of light, and
the radius of the cavity in which the fluorophore resides. n is the
refractive index and ϵ is dielectric constant. and are the wave-
numbers of the absorption and emission, respectively.
The solvent sensitivity of a fluorophore can be estimated by a Lippert
α
+
TAA [40]. 1NAT-CA and 9AAT-CA have lower Eonsets due to the
ν
A
​
ν
F
cyclohexyl group being an electron donating group. As shown in Fig. 7b.
9
AAT-6F, 9AAT-BA and 9AAT-CA show two pairs of redox peaks and
respond to two different colors change (in Fig. S7.). The two oxidation
peaks are produced in the two-step electrooxidation processes because
of the sequential conversion of cationic radical (polaron) and dication
plot. This is a plot of (
​
ν
A ꢀ
νF ) versus the orientation polarizability
(
) )
2
ε
ꢀ 1
n ꢀ 1
(
​
Δf =
ꢀ
2
​
(in Fig. 5b.). The sensitivity of these fluo-
2
ε
+1 2n +1
(
bipolaron) species [41]. The first oxidation peak is due to oxidation of N
rophores to solvent polarity linearly is due to a charge shift from the
amino group towards the electronegative carbonyl groups [38].
However, the obvious solvatochromic effect of 9AAT-6F and 9AAT-
BAis not observed which can be attributed to less contact and collision
between fluorophores and solvent molecules. The long relaxation time
of solvent molecules also reflects weak interaction between solvent
molecules and fluorescent molecules.
atom in TAA nucleus, and the second oxidation peak is most likely to
form a new oxidized derivative due to the recombination of the diradical
cation.
7

D. Li et al.
Dyes and Pigments 184 (2021) 108799
g
Fig. 8. (a) Calculated molecular orbitals of the model compounds. (b) E s of PAs.
3
.5. Quantum chemistry calculation
decrease, the TPA units and the fused ring groups are closer to the same
plane which enhances the electron transport ability between the fused
ring groups and the N atom of the TPA units. However, 1NAT-CA and
9AAT-CA with cyclohexyl are different from other PAs, because their
LUMO states located in the fused ring groups which cause ELUMOs and
As shown as in Fig. 8a, the electron cloud in the HOMO state of the
PAs is concentrated in the TAA moiety, and the electron cloud in the
LUMO state of 1NAT-6F, 1NAT-BA, 9AAT-6F and 9AAT-BA is distributed
in the hexafluoroalkyl group and the biphenyl group, respectively.
Especially, the electron cloud in the LUMO states of 1NAT-CA and 9AAT-
CA are distributed in the naphthyl group and the anthranyl group which
due to electron donating group of cyclohexyl. The numerical values of
HOMO and LUMO generally represent the ability of a molecule to supply
electrons and the ability to accept electrons, respectively. The twist
angles (θ) between TPA units and different fused ring groups were
calculated to explain the effect of molecular geometry on energy levels
and are shown in Table 3. The HOMO of PAs are located in the TPA
moiety and the fused ring groups are directly connected to the TPA units,
so that EHOMOs of PAs with the same TAA backbone increase with the
decrease of the twist angles. This is due to the fact that as the twist angles
E
g
s to be larger than other PAs. By comparing PAs containing different
fused ring groups, PAs with naphthyl group have smaller twist angles
and narrower E s than PAs with anthranyl group which perhaps because
g
naphthyl group connected to the TPA unit is a group with an asymmetric
structure. Combined with the propeller-like conformation of the TPA
molecule, it is speculated that the group introduced into the asymmetric
structure will have stronger molecular interaction, which hinders the
rotation of the naphthyl group [42]. The TPA units are connected to
fused ring groups with symmetric or asymmetric structure which will
cause changes in twist angles and the precise regulation of the molecular
structure and regulates the E
g
s (in Fig. 8b and Table 3.). The results also
indicate that electron transport within the polymer chain occurs from
8

D. Li et al.
Dyes and Pigments 184 (2021) 108799
Fig. 9. Electronic absorption spectra (a) of 9AAT-6F thin film in LiClO
4
/ACN solution upon different voltages. (b) The CIE1931 coordinate (X,Y). (c) Dynamic
changes of the transmittance and current. (d) Optical switching for 9AAT-6F.
Table 4
EC properties of the PAs.
a
c
d
e
2
PAs
λ
ΔT
(%)
Response
ΔOD
Qd (mC
CE (cm
b
ꢀ 2
ꢀ 1
Code
(nm)
time
cm
)
C
)
c
t (s)
b
t (s)
1
1
1
9
9
9
NAT-
815
843
828
798
821
811
17
15
25
39
38
21
3.55
2.69
2.79
3.01
4.19
2.97
3.76
3.73
2.48
2.66
2.62
3.79
0.12
0.14
0.24
0.31
0.57
0.25
0.69
1.25
1.64
1.17
3.98
1.97
174
112
146
265
143
126
6
F
NAT-
BA
NAT-
CA
AAT-
6
F
AAT-
BA
AAT-
CA
a
b
c
Maximum absorption wavelength of PAs films.
The time for the PAs film to reach90% of the full-transmittance change
.
Optical density (ΔOD)=log(Tb/Tc), where Tb and Tc are the transmittances in the bleached state
Fig. 10. PL changes of 9AAT-CA in the process of different potentials from 0 to
and colored state, respectively
1.2 V.
.
d
e
Qd is ejected charge
.
CE=ΔOD/Qd
.
the type of electrolyte and the impact of collisions between polymer and
solvent molecules and other effect together.
the ground state to the excited state. The CV experimental sequence of
E
g
s are 9AAT-CA > 9AAT-BA > 9AAT-6F and 1NAT-CA > 1NAT-BA >
NAT-6F, respectively which is most same as the theoretical calculation
3
.6. EC and EFC properties
1
data order of 9AAT-CA > 9AAT-6F > 9AAT-BA, 1NAT-CA > 1NAT-6F >
NAT-BA respectively. The deviation between the theoretical data and
The spectroelectrochemical properties of the PAs films are exhibited
1
by UV–vis spectrophotometer at the application of increasing potentials.
A typical electronic absorption spectrum of 9AAT-6F was measured in
the actual data of the two sequences is attributed to that the theoretical
calculation is based on the repeating structural unit of the polymer
rather than actual long chain of the polymer, contrary to that the actual
data is affected by the polarity of the solvent, the temperature of the test,
0
.1 M LiClO
4
/ACN as the electrolyte. No obvious absorption peak above
4
40 nm in the UV–Vis spectra under neutral state. When the voltage is
increased to 0.5 V, a significant absorption peak is observed at 798 nm
9

D. Li et al.
Dyes and Pigments 184 (2021) 108799
Fig. 11. (a) Changes in PL spectra of 1NAT-CA (2
μ
g/mL) under regularly TNP (0–36
μ
g/mL). (b) Correlation between TNP concentration and PL intensity. (c)
Frontier molecular orbital theory mechanism for TNP detection.
due to oxidation of the TAA unit. The voltage continues to rise to 0.9 V
when two absorption peaks are also visible at 560 nm and 611 nm due to
the recombination of radical ions. There is no further change in absor-
bance as the oxidation potential increases, indicating that the oxidation
potential has the maximum absorbance at 0.9 V (in Fig. 9a.). The
reversible change in color of PAs and the dynamic change of current
illustrate that the polymer has excellent cycle stability. After 100 cycles
of one thousand seconds, the transmittance and current have no obvious
downward trend, which further demonstrates that the polymer has good
cycle stability (in Fig. 9c.). And the 90% of the full bleaching time and
coloring time are 3.01 s and 2.66 s, respectively (in Fig. 9d.). The EC
coloration efficiency (CE) was calculated by formula (2) and (3):
unit and different carbonyl groups are used as acceptor units. The high
absorption and fast response time at lower oxidation potentials mean the
PAs have potential practical applications in EC devices or and displays
[43].
The EFC behavior was investigated by observing the PL with voltage
increasing continuously (in Fig. 10.). The polymer film shows strong PL
emission (λmax = 491 nm) in a neutral state. Due to the aggregation
effect, there is a significant hypsochromic shift in the solid state
compared to the solution state (located at 530 nm). As previously re-
ported by Leung, TAA groups have a PL quenching effect when they are
+
converted to TAA in oxidized state by application of a voltage. When
the voltage is applied from 0 V to 1.2 V, the intensity of the PL peak
gradually decreases to be zero nearly. Meanwhile, there is no significant
shift from the of PL peak position at the beginning to the final PL peak
position, indicating that there are no side-reactions during the process of
CE = ΔOD/Q
d
(2)
(3)
ΔOD = log (T
b
c
/T )
+
TAA to TAA conversion [44].
The CE of 9AAT-6F is calculated to be 265, corresponding in Table 4.
In the molecule, the side group of TAA is connected with anthryl group
has better electrical cycle stability than that is connected with naphthyl
by comparison. It is most likely due to the introduction of a larger vol-
ume of anthryl group, which causing a larger delocalization of the
electrons. The PAs are composed of TAA unit which is used as a donor
3.7. TNP detection
TNP solution with increasing concentrations was added to the PAs
solution with strong PL emission initially to investigate whether the PAs
solution had a sensitive response to analogues of explosive TNT. The
1
0

D. Li et al.
Dyes and Pigments 184 (2021) 108799
Fig. 12. (a) The PL intensity of the probe film (b) and UV–vis spectra changed after exposure to HCl and NH
3
. (c) The process of protonation and deprotonation of the
probe film. (d) The PL intensity of the probe film changed after ten cycles.
1
NAT-CA and 9AAT-CA (Conc.10
μ
M) in NMP solutions have strong PL
the self-quenching of PL prevents the diffusion of analytes into surface of
sensor and limits the application of solid detection materials as probe
films. 9AAT-6F solid film with high PL quantum efficiency can be used as
with λmaxs in 495 nm and 553 nm excited at 320 nm at room tempera-
ture, respectively. As the concentration of TNP which added to the PAs
solutions continuously is increased, the PL of the PAs solutions is
significantly quenched, which is attributed to the fact that TNP is a
strong electron acceptor that can effectively quench the PL of the donor
ꢀ 5
a sensor for detecting HCl gas. 9AAT-6F of concentration 1 × 10 mol/L
in NMP was uniformly drip-coated on a clean ITO glass followed by
being vacuum-dried to obtain a film. The PA film was exposed to HCl gas
resulted in PL quenching of the film. The shoulder peak at 382 nm
almost disappeared after exposure to HCl gas in the UV–vis spectra due
to the internal charge transfer (ICT) between the molecules and the in-
(
shown in Fig. 11a and Fig. S14.). Moreover an excellent linear corre-
lation is shown between the quenching rate (I /I-1) and concentration of
TNP in a lower concentration range (0–12 g/mL) (in Fig. 11b.). Stern-
Volmer quenching constant (Ksv) can be calculated according to formula
4) [45].
0
μ
tensity of the absorption peak at 309 nm caused by
π
-π* transition be-
(
tween aromatic ring (in Fig. 12b.) and nitrogen atom decreased
significantly and PL intensity decreased by 75% (in Fig. 12a.). Proton-
ation of the central N atom of TAA prohibits the internal charge transfer
of the molecule and causes PL quenching. Compared with other PAs that
do not show obvious specificity for HCl or the PL quenching of the films,
I
0
/I = 1+Ksv[Q]
(4)
4
By calculation, the Ksvs of 1NAT-CA and 9AAT-CA are 7.67 × 10
ꢀ 1
4
ꢀ 1
M
and 5.98 × 10 M , respectively. The mechanism of PL quenching
9
AAT-6F shows significant PL quenching when exposed to HCl due to it
can be better explained by the frontier molecular orbital theory. TNP is a
good electron acceptor which can improve the electron transport of the
polymer backbone. The LUMO level and HOMO level of 1NAT-CA are
has a large twist angle (in Table 3.) and the ICT process is obstructed
during the process of the PL quenching. When the doped film was
exposed to NH
a certain extent because the central N atom of TAA was deprotonated in
NH gas (in Fig. 12c.) [48]. The probe film has good cycle reliability and
3
again, the PL intensity of the probe film was recovered to
ꢀ
1.56 eV and ꢀ 4.66 eV (in Fig. 8.), respectively, and the LUMO of TNP
is ꢀ 3.74eV, which lies between the LUMO and HOMO of 1NAT-CA,
therefore it can provide sufficient power for the electron transfer in
the PL quenching process, causing the PL of 1NAT-CA to be dynamically
quenched by TNP [46,47]. A similar electron transfer process occurs
between TNP and 9AAT-CA (in Fig. 11c.).
3
the PL intensity of the film can still reach 70% of the initial value after
ten cycles (in Fig. 12d.).
4
. Conclusions
3
.8. HCl detection
Two new series PAs were synthesized successfully by direct poly-
The traditional method for detecting HCl is complicated and the
condensation reaction of TAA with dicarboxylic acids. Meanwhile, these
amorphous PAs have a wider range of potential applications, excellent
solvent properties and thermal stability. The influence of solvent po-
larity of TAA on PL emission spectra and aliphatic structure on the
background noise which will affect the detection and reduce the sensi-
tivity. PL based solid-state materials for gas detection has attracted great
attention. However, strong interaction among molecules which induces
1
1

D. Li et al.
Dyes and Pigments 184 (2021) 108799
spectral properties of PAs is discussed. Its EFC properties could be
adjusted through electrochemical oxidation processes, with high
contrast and good electrical cycling stability. 1NAT-CA and 9AAT-CA
could be used as sensors for explosives (TNP) with high sensitivity and
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Dongxu Li: Methodology, Investigation, Formal analysis, Writing -
original draft. Yan Yang: Methodology, Investigation, Formal analysis.
Caiyu Yang: Methodology, Investigation, Formal analysis. Wei Zhang:
Investigation. Yan Wang: Software. Xiaoxue Lin: Methodology. Yanyu
Gao: Investigation. Xinying Lv: Investigation, Formal analysis. Haijun
Niu: Writing - original draft. Wen Wang: Writing - review & editing.
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